The action of “sensing”, underlying operation of a sensor, is understood as an ability of the physical object to detect in real time changes in its physical/chemical environment and to translate these changes into a measurable signal such as an electric current.

Semiconductor materials and devices are uniquely suitable for sensing applications because, unlike metals and common insulators, several physical characteristics of semiconductors change in response to the changes of the physical or chemical characteristics of the ambient. As a result, semiconductor sensors, in various shapes and forms are at the core sensor technology.

It goeas without saying that without various types of sensors we wouldn't be evem close to where we are in terms of technical advancements. More later...

Recently, I came across a discussion regarding graphene solar cells. The term “graphene solar cell” implies the use of graphene as a material of which solar cell is constructed the same way inorganic (most notably silicon), organic semiconductors, or perovskite crystals are used (see earlier blogs). When used in this context, the term “graphene solar cells" seems to be somewhat misleading.

That is not to say there is no room for graphene in solar cells engineering. On the contrary, because of its distinct electrical, optical, and mechanical properties graphene is bound to play an important role in various solar cells, but rather as a part of the cell enabling its superior performance than the core material based on which cells are constructed. Whether in combination with other 2D materials (molybdenum disulfide MoS2 for instance), or with incorporation of graphene into the perovskite crystals, or with the use of graphene as a transparent, flexible contact material, there is no doubt graphene will serve various performance enhancing functions in solar cell technology. But should such cells be referred to as “graphene solar cells”? The term "graphene-based solar cells" seems to be better representing the concept of graphene use in solar cell engineering.

Since I’ve got into a brief overview of solar cells (see below), I cannot let it go without at least mentioning perovskite solar cells. Along with organic solar cells they represent emerging thin-film solar cell technology.

Perovskites are crystalline materials chemical composition of which may vary significantly, but which feature the same crystal structure as calcium titanium oxide CaTiO3 (perovskite structure). They have very good solar light absorption characteristics (it means they use large portion of the solar light spectrum) and matured into cells featuring above 20% efficiency. Overall. perovskite solar cells have a very good potential for low-cost large-scale commercialization.

In the case you are not all that familiar with perovskites check this site out.

Since 1989 I am involved in the organization of the International Symposium on Semiconductor Cleaning Science and Technology, SCST, under the auspicies of the Electrochemical Society. This time, symposium will be held during the ECS meeting in Atlanta, GA, Oct. 13-17, 2019.

Go to this site and check symposium G01 if interested in this topic. Or may be considering submitting an abstract? Abstarct submission site is now open

In the new generation photovoltaics special role is played by organic solar cells, or in other words, solar cells manufactured using organic semiconductors.

Organic solar cells are squarely at the other end of the efficiency paradigm than high-end solar cells solar cells mention earlier, but due to some unique features and low cost are bound to play a role on the photovoltaics arena.

Similarly to OLEDs (organic light-emitting diodes) the mechanism of light conversions into electricity is here somewhat different than in the case of inorganic semiconductor cells discussed earlier. In spite of the efficiency in the range of just few % in the basic version (efficiency increases even up to some 15% for more structurally complex configurations) and issues with stability when exposed to sunlight and elements, low-cost of organic cells combined with flexibility and transparency of the organic solar panels allows their uses in specialized applications where mostly rigid, opaque substrates based inorganic cells cannot be used.

See brief comments regarding perovskite solar cells which are in some ways similar to organic cells coming soon.

As indicated earlier, silicon serves very well "mass photovoltaics". However, in order to meaningfully increase efficiency of solar cells, multi-junction, compound semiconductors-based cells known as tandem solar cells are being employed.

The goal is to improve the use the solar spectrum by stacking up semiconductors featuring different energy gaps in multi-junction cells arranged such that energy gap width increases from the bottom to the top of the stack. This arrangement assures absorption of the fairly broad range of wavelengths included in the solar spectrum with shortest being absorbed by the top layers and longer penetrating deeper into the stack where they are absorbed by the narrower bandgap materials. The result is high-cost class solar cells, but also the cells featuring the highest efficiencies approaching 50%.

In reference to the previous entry... Vast majority of solar cells is manufactured using silicon (in the order of decreasing efficiency either single-crystal, or multicrystalline, or amorphous depending on the needs) which is on one hand by far the most common and highly manufacturable semiconductor material, and on the other features energy gap which sufficiently well matches energy spectrum of the sunlight.

All in all, silicon very well serves the needs of photovoltaic industry and we are very lucky to have this outstanding element so readily available (sand!).

As mentioned in previous entry, solar cells come in the variety of shapes. A question is what type of cell is used where?

The choice is based on various criteria. For instance, what is the area available and how it defines the cost of the cells, and thus, materials/methods used to manufacture them? Is it a several square miles big part of the desert or few square meters wide satellite panel? Or maybe less than centimeter square cell powering a wrist watch or calculator? In the first case cost is an issue because such a solar farm is meant to produce energy at the cost comparable with the energy obtained from other sources. In the second case cost is not an issue because at whatever cost the highest efficiency solar cells must be used. In the third case the cost of the cell is marginal and is not even a consideration.

Semi1source.com/blog is the personal blog of Jerzy Ruzyllo. With over 35 years of experience in academic research and teaching in the area of semiconductor engineering (currently holding position of a Distinguished Professor of Electrical Engineering and Professor of Materials Science and Engineering at Penn State University), he has a unique perspective on the developments in this progress driving technical domain and enjoys blogging about it.

With over 2000 terms defined and explained, Semiconductor Glossary is the most complete reference in the field of semiconductors on the market today.